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Terry Again
11-26-2008, 07:14 AM
Hi All,
And In My search I haven't found a source for single Schottky Diodes used to reduce voltage! Anyone know of any source for them I can't afford to have 30,000 made and sit on them till they hatch!!:-) Or should I just go with the expensive alternitive wien cell battery? Any one out there use those tell me how long they last in use? It's always sumpthin'!! Or should or could I just have the meter in the SRT calabrated to use the 1.55 volts of the Silver oxide battery? Or is there a problem with doing that my brain damaged mind has failed to see?
ALSO Anyone Know if a Minolta XD11 calabrated to use alkaline bateries at 1.5 volts would have a messed up metter IF one used the proper Silver oxide batteries in it at 1.55 volts? Or is this the wrong place for these questions???
I'm sorry about my spelling also my phoenetics sucs! :-)

Terry

Steve Smith
11-26-2008, 07:21 AM
I can probably find some BAT54 diodes I could send you. They are surface mount SOT23 package but I could add some wires to them.

Datasheet here: http://www.fairchildsemi.com/ds/BA/BAT54.pdf

If you want some, send me your postal address by PM.



Steve.

bsdunek
11-26-2008, 07:53 AM
I use Wein cells in my Nikon FTN's and Gossen meters. They last nearly a year - depending on use. I buy them by the carton of 12 from Micro Tools. I think this is the easiest replacement for the PX13 & 625.
http://www.micro-tools.com/store/item_detail.aspx?ItemCode=MRB625-12

Ralph Javins
11-26-2008, 02:30 PM
Good morning, Terry;

The Silver-Oxide batteries have a much more stable discharge curve. Their voltage stays nearly the same over their useful life. Not exactly, but similar to the old Mercury battery, but at a slightly higher voltage. The alkaline batteries will have a constantly decreasing voltage that will affect the light meter reading by a constantly changing amount. At least with the Wien cells and the Silver-Oxide batteries, if the light meter reading is off, it will be off by a fairly predictable amount, so you can compensate if required. Often the lightmeter circuit can be adjusted to work with the 1.55 VDC batteries.

There are many sources for Schottky Barrier Diodes. Radio Shack did have them in the past. Jameco Electronics. Digikey. All Electronics Corporation. RF Parts. Mouser Electronics. Ocean State Electronics. Frye's Electronics. Newark Electronics is still there, but the minimum order amount may not be palatable. There are still people who are selling bits and pieces.

Terry Again
11-26-2008, 06:51 PM
That doesn't look like the Diode listed in the srt pages at the Rokker something? My brain damage just kick in big time can't remember the name of the site now but they have the mod to silver oxide and it lists 1n7511 Schokkty Diode? Maybe what you have does something differently? What do I know? I get to know IF your pieces would work to lower voltage from 1.55 to 1.35 I'm all eyes!! :-) Interested that is Kind sir!
Have a good one,
terry

Nicholas Lindan
11-26-2008, 07:34 PM
Try looking for an 1n5711 Schottky... http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=497-2499-1-ND $0.46 each.

chriscrawfordphoto
11-26-2008, 07:50 PM
Try looking for an 1n5711 Schottky... http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=497-2499-1-ND $0.46 each.

Thanks for the info. I had been looking for those, and every place I found wanted to sell 1000 of them at a time. Radio Shack didn't carry any of the ones that work for cameras. I just ordered a pack from Digikey.

Steve Smith
11-27-2008, 02:56 AM
I get to know IF your pieces would work to lower voltage from 1.55 to 1.35 I'm all eyes!!

The BAT54 drops just under 0.2v at minimal currrent. The one I measured was 0.196v so would be ideal.

I have some here with wires attached and encapsulated in a bit of heat shrink tubing if you want them.


Steve.

Terry Again
11-27-2008, 09:28 AM
Hi All,
Steve I thank you for your kind offer and I think I shall see what happens on this side of the pond first? I still have to thank Nick for the link at Digi key that I missed while there!! Next is the 47 dollars shipping and handling charges!! It's the American Way!! And I still have to find and compare the discharge voltchange on the Silver oxide as compared to the wein cell ones? And find out the cost of the diode mod to the camera etc........ to make a true comparasion between the 2 types? And how long each kind last in use? Anyone out there in Minolta users land know? I thank you all for the replies on this question!!

Rod Downes
11-28-2008, 05:19 AM
Terry,
I did this mod to my SRT's some time ago (using the quoted IN5711 diode which I obtained off ebay) and it works great using silver oxide cells.I find silver oxide cells best - I find they last between 3 and 5 years in my SRT.Here is a link to the SRT battery mod at Anthony Hands' Rokkor Files
site.In the first section there is a graph showing discharge profiles of the different types of cell.
http://www.rokkorfiles.com/Dickspages.htm
Hope this is useful.
Rod Downes

Nicholas Lindan
11-28-2008, 08:39 AM
Silver oxide batteries are available in two types. For Energizer batteries the better style is the 'H' series, examine
the discharge curves:
http://data.energizer.com/PDFs/357-303H.pdf
http://data.energizer.com/PDFs/357-303.pdf

Likewise the 'SR44' and 'SR44W' are preffered over the 'SR44SW'.

The distinction seems to be the electrolyte, KOH providing a flatter discharge than NaOH.

Terry Again
11-28-2008, 04:16 PM
That's like 2 different batteries!! I will go for the 357H when it's time! What's this SR44 and SR44W refer to? I guess batteries as that looks familar from a different camera I had? I do thank you for the info and help you given me on this conversion I'm about to try? It is a simple procedure yes? Do you think I should have the camera's meter checked after having this done to see how correct it is?
Have a good one,

crabby
11-28-2008, 08:15 PM
Forgive me if this is a dumb question, but why not just use 1.5v batteries and re-adjust the film speed accordingly? ISO 100 at 1.35v becomes a meter setting of ISO 25 at 1.5v.

Does higher voltage damage the meter?

I shoot this way with a Miranda Sensorex and it works fine in EE-auto and manual mode.

Terry Again
12-01-2008, 07:59 AM
I don't think there are dumb questions in life just dumb answers!! That said I must ask where the formula came from to make the adjustment of the camera setting for film speed? And I would have to wait for others to answer on the possible damage caused by higher voltage? Though I have to wonder as It's not a lot of difference but then I am brain damaged and have been very wrong in the past on things!! I will at least see how much it cost to have a pro add the diode to the battery circuit and hope I can afford it before the mercury battery goes dead! Or as my Friend in NZ would say suck a Kumara!! Any other replies?

Nicholas Lindan
12-01-2008, 10:01 AM
The difference in battery voltages will cause no damage to any electronics. Camera meters operate at minuscule power levels, even if the voltage is raised by by the use of the wrong battery the extra 3 millionth of a watt isn't going to do anything. Voltages have to rise quite a bit higher to damage any integrated circuits and such, and most old cameras use only resistors and a meter.

How the camera responds to a change in battery voltage depends on the design of its meter. Older stop-down meters that center the needle should be relatively oblivious to any change in battery voltage. How well open aperture meters will work with an adjustment to the ASA depends on the design of the meter: simple meters may work over a wide range of light intensities; very sensitive meters with linearizing and amplifying circuits may need different ASA adjustments for low light and bright light.

Adjusting the ASA to compensate for battery voltage is a workable solution that works better with some cameras than others.

All of which is no news.

crabby
12-01-2008, 02:52 PM
That said I must ask where the formula came from to make the adjustment of the camera setting for film speed?

I recalibrate the ISO setting as follows.

Bright sunny day, ISO 100 film, we all know the setting will be f16 at 1/125th.

I insert a 1.5v battery in place of the required 1.35v battery.

Adjust your meter setting to see which ISO setting tells you to shoot at f16 @ 1/125th.

In most cases I have found a setting of ISO 25 at 1.5v equals a setting of ISO 100 using 1.35v.

Crayguns
12-02-2008, 09:04 PM
For what it's worth
I have SRTs and some other cameras the were built for mercury cells. The Wein cell is a zinc air cell.
What works for me though is Walgreen's 675 Premium Zinc Air hearing aid batteries. They put out 1.4 volts. They have a smaller diameter than the Weins. Take your camera to the car parts or hardware store and get an O-ring to fit inside the battery compartment and surround the 675 cell. This set-up works great for me.

John Hermanson
12-03-2008, 03:29 PM
IN-6263 schotkey diodes. Drops the 1.55v of silver oxide batteries to approx.1.35v. I've used them for years in the Olympus OM-1/1N. When you test the meter with your calibrated light test box, you'll see that the meter is linear though it may need a little tweeking through the regular adjustment method. Absolute accuracy may not be that critical if you are shooting color negative film (which has a wide exposure tolerance). If you need a couple of these diodes, $1 each + $8 S&H. Pay by paypal if you like., John, www.zuiko.com

Changeling1
12-03-2008, 03:53 PM
One of the best things about the SRT's is they don't need no stinkin' batteries... ;)

2F/2F
12-03-2008, 04:09 PM
Wrap a 1.4V alkaline 675 hearing aid battery in a correctly sized split washer to take up the empty space and there you have it; the best practical 625 replacement option. They are perfectly accurate and they are *dirt* cheap too. I buy them anywhere in multi packs of five for $3. I find them much more accurate, consistent, long lasting, and economical than Wein cells, which I used for years before a repairman tipped me off to the 675 method. Going this route not only gives better results, IMO, but also lowers the yearly cost per camera to about $1.20 (changing every six months), where it was about $24 per year per camera using Wein cells (changing every three months). With four Canon FD bodies, a Nikon F Photomic T, and a Canon FTb low light booster, I was going through Wein cells like mad, and results were all over the place. None of my cameras ever matched my spot meter or each other with Wein cells. Not so with the 675s.